The present invention relates to a magnetic material, and more particularly to a magnetic alloy film suitable for use in high-density magnetic recording and reproduction, which is required in digital video tape recorders (VTR's) and high-resolution VTR's and to a magnetic head using such a film.
A material for a core of magnetic heads has been required not only to have a high saturation flux density (Bs) but also to excel in hardness, corrosion resistance and thermal stability for soft magnetic properties. Conventionally, the cores of magnetic heads have been made of ferrite, sendust and Co-based amorphous material among others. The Bs levels of these materials, however, are only about 5 kG for ferrite, 10 kG for sendust and 8 kG for Co-based amorphous material and, thus, a material with a higher Bs level has been further called for to realize stable performance of high-density magnetic recording and reproduction.
In this connection, there is a recent report on a favorable soft magnetic film made of an alloy having a composition of FeMC (M:/Zr, Ti, Hf, Ta, Nb), having a Bs level of about 16 kG (Technical Report of the Society of Telecommunications, MR89-12 (1989)). This FeMC-based film, however, involves such problems yet to be solved as (1) susceptibility to rust because of its much carbon content, (2) insufficient hardness and the resultant low wear-resistance and (3) inability to provide a satisfactory soft magnetic alloy film surpassing 17 kG in a Bs level.
With a view to solving these problems, there has been proposed in Japanese Patent Laid-Open Publication No. 54-229408 (229408/1989) a magnetic alloy film having the composition of FexMyNz, where M is at least one metal selected from a group of Zr, Nb, Hf, Ta, Mo and Ti, N is nitrogen, x, y, and z represent atomic percentages, 65.ltoreq.x.ltoreq.94, 5.ltoreq.y.ltoreq.25, 3.ltoreq.z.ltoreq.20, and x+y+z=100.
Incidentally, the soft magnetic properties of the FexMyNz film is thermally stable in the range of about 550.degree. to 550.degree. C. Therefore, during glass deposition to process this film into a video head, the temperature cannot be raised beyond this range, leaving the glass still viscous and adversely affecting the product quality and yield. In order to achieve improvements in these respect, the thermal stability of the film should be further raised. In other words, a magnetic alloy film with greater thermal stability should be obtained.
SUMMARY OF THE INVENTION
An object of the present invention, therefore, is to provide a novel magnetic alloy film which has higher thermal stability and, thus, can contribute to raising the yield of head processing and the quality of the resultant heads.
Another object of the invention is to provide a magnetic head for use in VTR's, made of the above mentioned magnetic alloy film.
According to the invention, there is provided a magnetic alloy film having the composition of (FexMyNz)aLb, where M is at least one metal selected from a group of Zr, Nb, Hf, Ta, Mo and Ti, L is Cu and/or Ag, x, y, z, a and b represent atomic percentages, 70.5.ltoreq.x.ltoreq.84, 7.ltoreq.y.ltoreq.14, 9.ltoreq.z.ltoreq.15.5, x+y+z=100, 95.ltoreq.a.ltoreq.99.5, 0.5.ltoreq.b.ltoreq.5, and a +b=100.
Where the composition represented by x, y and z is achieved, there is obtained a superior soft magnetic alloy film whose Bs is 16 to 18 kG, the addition to which of Cu and/or Ag within the above stated range helps to make the crystalline grains even finer and to improve, in particular, the thermal stability of the soft magnetic properties. This result is presumably due to the fact that Cu and Ag have positive parameters of interaction with Fe, are low in solid solubility and tend to separate, so that, upon heating, either Fe atoms or Cu and Ag atoms gather by themselves to invite compositional fluctuation, and at this time the group of Cu and Ag atoms inhibits the growth of microcrystalline grains mainly consisting of Fe. The content b of Cu and/or Ag is within the range of 0.5 to 5 atomic %. If it is below 0.5 atomic %, the addition of Cu and Ag will have no significant effect to make the crystalline grains finer. On the other hand, if it is above 5 atomic %, the Bs and permeability will drop, which is undesirable. The especially desirable range of the content b of Cu and/or Ag is between 0.5 and 5 atomic %, within which a particularly satisfactory soft magnetic alloy film can be obtained, and the thermal stability of its soft magnetic properties is enhanced.